Optical discs, of which DVDs (Digital Versatile/Video Discs) are representative, have become common as recording media for recording large amounts of digital data, such as AV (audio/video) data and computer data. For example, playback-only optical discs having two hours or more of high-quality moving images recorded thereon are on the market. Such digital data that is subject to copyright is called a digital copyrighted work (hereinafter referred to simply a “digital work”).
In recent years, content scrambling systems have been introduced to prevent digital works being copied illegally to other recording media. For descriptions of such systems, refer to Makoto TATEBAYASHI et al., “DVD Content Scramble System”, ITE Technical Report Vol. 21, No. 31, pp. 15-19, VIR '97-26 (May, 1997), and NIKKEI ELECTRONICS, Nov. 18, 1996 (No. 676), pp. 13-14.
A content scrambling system scrambles compressed digital content, such as a movie, with use of three layers of secret keys (a title key, a disc key and a master key), and records the scrambled data on an information recording medium in a user information area that is accessible by a user.
The most important of the secret keys, the master key, is known only to manufacturers who have a legitimate license. The disc key and the title key, which are unique to each DVD and each title respectively, are scrambled based on the master key and stored on the information recording medium in a control information area that is not accessible by the user. This restricts access by the user to the secret keys that are necessary for unscrambling, and therefore prevents the digital content being copied illegally by means such as copying files.
The focus of research and development in the field of scrambling in recent years has been moving away from copyright protection for protecting copyrighted information and towards copyright control that provides digital copyrighted works conveniently for the user.
SD memory cards, which are semiconductor memories, are exemplary of such convenience for the user. Such an information recording medium (hereinafter referred to simply as a “recording medium”) is provided with a protected area in addition to the user area. The protected area, which is accessible only by the system, stores copyright management information relating to rights for moving, copying, or the like, of the corresponding digital work. This enables the digital work to be moved or copied within the scope of the rights.
FIG. 1 illustrates a method proposed in Japanese patent no. 2981448 for one type of copyright management, specifically, moving a digital work between recording media when the recording media do not have protected areas for recording copyright management information.
This method realizes safe movement of a digital work by first moving the digital work that is recorded in a recording area 2003 of a first medium 2001 to a recording area 2005 of a second medium 2002, and then deleting management information 2004 of the first medium 2001 that includes position information of the recording area 2003.
However, in this method, the digital work can be moved freely, and it is not possible to control, for example, the number of times that the digital work is permitted to be moved. Furthermore, even if the move times is managed by recording such information in the user area, the user may tamper with the information. If usage rights of a digital work recorded on an optical disc are to be controlled, it is necessary to provide a protected area such as described for semiconductor memories on the optical disc.
To provide a protected area that is not accessed by the user, it is impossible to use a physical medium efficiently. Furthermore, in order to implement rights management in a recording medium, such as an optical disc, that does not have a protected area for recording copyright management information, it would be necessary to change the specifications of the recording medium itself. For these reasons, rights management is not presently implemented in such recording media.
The object of the present invention, which solves this problem, is to provide a recording medium that prevents a digital copyrighted work that is recorded thereon from being copied exactly as is, and, even in a recording medium that does not have a separate protected area, enables rights management of recorded digital copyrighted works; and an usage method for the recording medium.